It is a wrong assumption that the speed of sound decreases
with altitude above sea level, because the density of air
decreases with height. The changing of atmospheric pressure
does not change the speed of sound.Only the colder temperature (!) lets decrease the speed of
sound at higher altitudes.The speed of sound has nothing to do with "sea level".
For sound pressure without the medium air there is no speed
of sound.Speed of sound is dependent nearly only on its temperature.It is not dependent on the sound amplitude, frequency, orwavelength.

The speed of sound in air c is determined by the air itself and is not dependent
upon the amplitude, frequency, or wavelength of the sound.For an ideal gas the speed of sound depends only on its temperature and is
independent of gas pressure. This dependence also applies to air, in good
approximation and can be regarded as an ideal gas.This is a site for sound engineers and musicians. We are interested in the
speed of sound of air (!) on Earth at places where acoustic musical instruments
or voices are used, usually in rooms or halls. The speed of sound of
atmospheric layers, as in 100 km altitude (height), or close to the vacuum is not
of interest.
Also we do not care about higher air pressure in car tires.
Which speed does sound in our usual life have?

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What is the speed of sound in air?
Speed of sound depends only on
the temperature of the air.

Forget the air pressure!
"At sea level" is not correct.

Select the temperature unit
and enter the air temperature:

The speed of sound c is:
(propagation speed)

m/s

Celsius

km/h - not kmh!

Fahrenheit

mph miles per hour

kelvin

ft/s feet per second

Rankine

knots

Notice for musicians and technicians (not for professors of physics):The speed of sound in air changes clearly with temperature, a little bit with
humidity − but not with air pressure (atmospheric pressure) and height.The words "sound pressure at sea level" are incorrect and misleading in
the case of "speed of sound". The temperature indication, however, is
absolutely necessary.The changing of atmospheric pressure does not change the sound
of musical instruments in a concert hall or in a room.
That does the changing of temperature.

The average air pressure at sea level is 101325 Pa. However, this information is
insignificant for the speed of sound. We always need the specification of the temperature.

In SI units with dry air at 20°C (68°F), the speed of sound c is 343 meters per second (m/s).
This also equates to 1235 km/h, 1125 feet per second (ft/s or fps), 666 knots, 767.3 miles
per hour (mi/h or mph), 12.79 miles per minute (mi/min), 0.2131 miles per second (mi/s),
That is 0.343 kilometers per second (km/s), or 20.58 kilometers per minute (km/min).
It makes no sense to give the speed of sound adding the words at the "standard atmosphere at sea level".
To get the speed of sound the temperature is important, not the barometric pressure.Statement: The static air pressure p_ and the density ρ of air (air density) are proportional at the same
temperature, because the ratio p_ / ρ is always constant, on a high mountain or even on sea level altitude.Notice: The ratio p_ / ρ (static air pressure to air density) is really always constant. Formula:

Speed of sound

That means, the ratio p_ / ρ is always constant on a high mountain,
and even at "sea level". The static atmospheric pressurep_ and the
density of air ρ go always together. The ratio stays constant.When calculating the speed of sound forget the atmospheric pressure,
but look accurately at the very important temperature.
The speed of sound varies with altitude (height) only because of the
changing temperature there.
Pressure is dependent on temperature and indirectly on altitude.

Adiabatic index or ratio of specific heats κ (kappa) = cp / cv = 1.402 for air.Specific heat in a constant pressure process = cp; Specific heat in a constant volume process = cvGenerally we take with sufficient accuracy the formula (equation) for the speed of sound in air
in m/s vs. temperature ϑ (theta) in degrees Celsius (centigrade):

A change of temperature of Δ ϑ = 1°C is equal to
a change of the speed of sound of Δ c = 60 cm/s.

There is a useful formula (rule of thumb) to get the temperature ϑ in °Cwhen you know the speed of sound c in air (m/s).Formula: Temperature of air ϑ ≈ (c − 331.3) / 0.6 in °C.With the following formula you can calculate exactly the speed of sound.Speed of sound in m/s;
temperature ϑ in °C.

Speed of sound vs height and temperature?Forget the height and take care only about the temperature.

At the temperature of ϑ = 0°C the speed of sound in dry air was determined to bec = 331.3 m/s.0°C equals 68°F.Exact equations for speed of sound and temperature:To calculate accurately the speed of sound in m/s:c = 331.3 × √ (1+(ϑ / 273.15))if one uses the known temperature of air ϑ in °C.To calculate accurately the temperature of air in °C:ϑ = 273.15 × (0.0000091108129040816350702156684298215 × c2 − 1)if one uses the known speed of sound c in m/s.

The speed of sound c depends on the temperature of air ϑ and not on the air pressure!
The humidity of air has some negligible effect on the speed of sound. The air pressure
and the density of air (air density) are proportional to each other at the same temperature.
It applies always p / ρ = constant. rho is the density ρ and p is the sound pressure.
Therefore air pressure does not enter the calculation of the speed of sound of air.

Notice: The speed of sound is alike on a mountain top as well
as at sea level, provided that there is the same air temperature.It can be assumed that this is true even at 100 km altitude.
With decreasing pressure, the density of air decreases.

At what temperature the speed of sound is double its value of 0°C?

At which temperature the speed of sound 331.3 m/s (velocity of sound) will be doubled?
A temperature of 819.45°C will double the speed of sound to 662.6 m/s.

The speed of sound is called Mach 1Mach is commonly used to represent an object's speed, such as an aircraft
or a missile, when it is travelling at the speed of sound or at multiples of it.
The speed higher than Mach 1 is called supersonic speed.

Mach number below 1 means the flow velocity is lower than the speed of sound - and the speed is subsonic.
Mach number 1 means the flow velocity is the speed of sound - and the speed around that is transonic.
Mach number above 1 means the flow velocity is higher than the speed of sound - and the speed is supersonic.
More than Mach number 5 is called hypersonic. The "Mach number" is a dimensionless ratio.

Note: The speed of sound c is independent of the frequency and the
amplitude of the sound wave, and the air pressure. But the speed of
sound is dependent on the temperature.At a temperature of 819.45, we get a speed of sound of 662.6 m/s.
That is double the speed of sound, we find at 0°C with 331.3 m.

The supersonic speed has absolutely
nothing to do with the air pressure – but
with the temperature!The density ρ of the air also has no effect,
because the ratio of the air pressurep to
the densityρ that is p / ρ is always
constant. Look at this important formula:

Speed of sound

Table (chart): The impact of temperatureThe air density, the speed of sound, the characteristic acoustic
impedance and the dependency of the temperature of air

Temperature
of air ϑ in °C

Speed of soundc in m/s

Time per 1 mΔ t in ms/m

Density of airρ in kg/m3

Impedance
of air Z in N·s/m3

+40

354.94

2.817

1.1272

400.0

+35

351.96

2.840

1.1455

403.2

+30

349.08

2.864

1.1644

406.5

+25

346.18

2.888

1.1839

409.4

+20

343.26

2.912

1.2041

413.3

+15

340.31

2.937

1.2250

416.9

+10

337.33

2.963

1.2466

420.5

+5

334.33

2.990

1.2690

424.3

0

331.30

3.017

1.2920

428.0

−5

328.24

3.044

1.3163

432.1

−10

325.16

3.073

1.3413

436.1

−15

322.04

3.103

1.3673

440.3

−20

318.89

3.134

1.3943

444.6

−25

315.72

3.165

1.4224

449.1

Notice: Air pressure p and air density ρ are not the same.
In gases, the higher the speed of sound in that medium, the higher the pitch will be, when you sing.

Only because of the decreasing air temperature, which decreases with altitude (height), the speed of sound decreases.

In conventional use and in scientific literature sound velocity is the same as speed of sound or acoustic velocity.Sound velocity c should not be confused with sound particle velocity v, which is the velocity of the individual particles.

Approximate speed of sound
in common materials

Medium

Speed of sound
m/s ft/s

Air, dry at 20°C

343

1 125

Hydrogen at 0°C

1 280

4 200

Water at 15 °C

1 500

4 920

Lead

2 160

7 090

Concrete

3 100

10 200

Wood (soft - along the fibre)

3 800

12 500

Glass

5 500

18 500

Steel

5 800

19 000

In a given ideal gas the speed of sound depends only on its temperature.
The speed of sound in still dry air at a temperature of ϑ = 0 degrees
Celsius is c = 331.3 m/s.
It depends on the temperature and material. Since sound is transferred
easily through densely packed molecules, it is faster in denser
substances.
Thus the speed of sound increases with the stiffness of the material.

On the frequent question: "How much is the speed of sound?" must always follow
the demand: "At what temperature, please?"
Who mentions the barometric pressure, has still something to learn.

Speed of sound and acoustic velocity (velocity of sound)

Speed is the rate of change of distance with time.
Velocity is a measure of both speed and direction of a moving object.
Velocity is the rate of change of displacement with time.
Speed is a distance an object goes, velocity is measurement of speed AND direction.

In a given ideal gas the sound speed depends only on its temperature. The speed of
sound in still air at 0 degrees Celsius is 331.3 m/s. It depends on the temperature, and
the material. Since sound is more easily transmitted between close molecules, it travels
faster in the denser substance. Thus the speed of sound increases with the stiffness of
the material.

Really wrong answers at "Yahoo! Answers"

How does the speed of sound in air depend on air pressure?1st wrong answer: Best Answer - Chosen by Voters
Thinner air has less atoms floating around in it than denser (higher pressure) air.
Since sound waves travel faster when unimpeded, less air pressure equates to
faster speed due to decreased atmospheric 'viscosity'.
2nd wrong answer: Speed of sound in air is directly proportional to the square root
of pressure.
The correct answer is: The speed of sound does not depend on air pressure, but
on temperature. Air pressure is not the same as density of air.

To use the calculator, simply enter a value.
The calculator works in both directions of the ↔ sign.

Temperature ϑ (theta)
°C

↔

Speed of sound v
m/s

Frequency f
Hz

↔

Wavelength λ
m

At 0° Celsius the speed of sound in U.S. textbooks is 331.3 m/s.
At 20° Celsius the speed of sound then is 343.21 m/s, rounded 343 m/s.
At 0° Celsius, the speed of sound in German textbooks is 331.5 m/s.
At 20° Celsius the speed of sound then is 343.42 m/s, rounded 343 m/s.

Speed and Velocity - The Difference

Speed is the distance in a certain period of time.
Velocity is a measure of both speed and direction of a moving object.
Difference: Speed is a distance an object goes in unit time.
Velocity is displacement made in unit time.
Difference: Speed is a scalar quantity – it has only magnitude and cannot
be zero.
Velocity is a vector quantity – it has both magnitude and direction and it
can be zero.

To use the calculator, simply enter a value.
The calculator works in both directions of the ↔ sign.

Temperature in Fahrenheit:
°F

↔

Temperature in Celsius:
°C

°F = °C × 1.8 + 32

°C = (°F − 32) / 1.8

Sound pressure or acoustic pressure is the local pressure deviation from the ambient
atmospheric pressure caused by a sound wave. Sound pressure can be measured using
a microphone in air. The SI unit for sound pressure p is the pascal − symbol: Pa.

NASA says: The speed of sound is dependent on the temperature of the air.
It varies with altitude (height) only because of the changing temperature!
The atmospheric pressure is proportional to the density of air.
Therefore both values have no effect on the speed of sound.

The speed of sound in air at 0°C can be calculated asc = (1.4×(287.058 J/K·kg)×(273.15 K))^1/2 = 331.3 m/s,
where κ (kappa) = 1.4 and the
specific gas constant for dry air R = 287.058 (J/K·kg).
The speed of sound in air at 20°C can be calculated asc = (1.4×(287.058 J/K·kg)×(293.15 K))^1/2 = 343.24 m/s.

Zonal mean vertical profile of temperature in
the atmosphere during June at 45° NorthTemperature vs. Height (Atmospheric Pressure)

Wrong thinking:Calculate speed of sound at high elevations.
You feel the assumption that this must have to do with height. That is wrong.
Only the temperature has to do with the value of the speed of sound.
It's pretty cold above there.

The sound pressure or acoustic pressure (alternating pressure changes) is a
dynamic pressure. However, the air pressure (atmospheric equal pressure) is
a static pressure. The dynamic sound pressure is superimposed on the static
air pressure.

Note: Time, frequency and phase belong close together.
The height of the amplitude has no influence on those parameters.The amplitude A has nothing to do with the frequency, the wavelength,
the time duration and the speed of sound.